104 lines
4.9 KiB
HTML
104 lines
4.9 KiB
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<html lang="en">
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<title>MiniDebugInfo - Debugging with GDB</title>
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<meta name="description" content="Debugging with GDB">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="GDB-Files.html#GDB-Files" title="GDB Files">
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<link rel="prev" href="Separate-Debug-Files.html#Separate-Debug-Files" title="Separate Debug Files">
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<link rel="next" href="Index-Files.html#Index-Files" title="Index Files">
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Copyright (C) 1988-2019 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``Free Software'' and ``Free Software Needs
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Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
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and with the Back-Cover Texts as in (a) below.
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(a) The FSF's Back-Cover Text is: ``You are free to copy and modify
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this GNU Manual. Buying copies from GNU Press supports the FSF in
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<body>
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<div class="node">
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<a name="MiniDebugInfo"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Index-Files.html#Index-Files">Index Files</a>,
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Previous: <a rel="previous" accesskey="p" href="Separate-Debug-Files.html#Separate-Debug-Files">Separate Debug Files</a>,
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Up: <a rel="up" accesskey="u" href="GDB-Files.html#GDB-Files">GDB Files</a>
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<hr>
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</div>
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<h3 class="section">18.4 Debugging information in a special section</h3>
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<p><a name="index-separate-debug-sections-1290"></a><a name="index-g_t_0040samp_007b_002egnu_005fdebugdata_007d-section-1291"></a>
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Some systems ship pre-built executables and libraries that have a
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special ‘<samp><span class="samp">.gnu_debugdata</span></samp>’ section. This feature is called
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<dfn>MiniDebugInfo</dfn>. This section holds an LZMA-compressed object and
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is used to supply extra symbols for backtraces.
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<p>The intent of this section is to provide extra minimal debugging
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information for use in simple backtraces. It is not intended to be a
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replacement for full separate debugging information (see <a href="Separate-Debug-Files.html#Separate-Debug-Files">Separate Debug Files</a>). The example below shows the intended use; however,
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<span class="sc">gdb</span> does not currently put restrictions on what sort of
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debugging information might be included in the section.
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<p><span class="sc">gdb</span> has support for this extension. If the section exists,
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then it is used provided that no other source of debugging information
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can be found, and that <span class="sc">gdb</span> was configured with LZMA support.
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<p>This section can be easily created using <samp><span class="command">objcopy</span></samp> and other
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standard utilities:
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<pre class="smallexample"> # Extract the dynamic symbols from the main binary, there is no need
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# to also have these in the normal symbol table.
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nm -D <var>binary</var> --format=posix --defined-only \
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| awk '{ print $1 }' | sort > dynsyms
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# Extract all the text (i.e. function) symbols from the debuginfo.
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# (Note that we actually also accept "D" symbols, for the benefit
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# of platforms like PowerPC64 that use function descriptors.)
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nm <var>binary</var> --format=posix --defined-only \
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| awk '{ if ($2 == "T" || $2 == "t" || $2 == "D") print $1 }' \
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| sort > funcsyms
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# Keep all the function symbols not already in the dynamic symbol
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# table.
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comm -13 dynsyms funcsyms > keep_symbols
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# Separate full debug info into debug binary.
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objcopy --only-keep-debug <var>binary</var> debug
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# Copy the full debuginfo, keeping only a minimal set of symbols and
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# removing some unnecessary sections.
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objcopy -S --remove-section .gdb_index --remove-section .comment \
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--keep-symbols=keep_symbols debug mini_debuginfo
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# Drop the full debug info from the original binary.
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strip --strip-all -R .comment <var>binary</var>
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# Inject the compressed data into the .gnu_debugdata section of the
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# original binary.
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xz mini_debuginfo
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objcopy --add-section .gnu_debugdata=mini_debuginfo.xz <var>binary</var>
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</pre>
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</body></html>
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